Process for preparing porous electrolytic metal foil

ABSTRACT

A method of manufacturing a porous electrolytic metal foil, in which a thin metal layer is formed by electrically depositing a metal on the surface of a cathode body by moving the cathode body through an electrolyte. The thin metal layer is separated from the cathode body to form an exposed surface on the cathode body and a film of an electrical insulating material is formed on the exposed surface of the cathode body, by spraying a resin liquid onto the exposed surface, or by suspending machine oil or insulating oil in the electrolyte. The metal foil thus produced has many open-pores in the thickness direction. Therefore, when the metal foil is used as a collector for a battery electrode, there is an improvement in the cycle life characteristics of the battery.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a porouselectrolytic metal foil and, more particularly, to a method ofmanufacturing a porous electrolytic metal foil in which when the metalfoil is used as a collector of secondary battery, a mixture forelectrode can be supported firmly on the collector, and electrontransfer reaction can be caused uniformly at the charging/dischargingcycle time.

BACKGROUND ART

In recent years, as portable electronic equipment such as video camerasand notebook type computers has widely been used, the demand for smallhigh-capacity secondary batteries has increased as power sourcestherefor. Most of the secondary batteries now being used arenickel-cadmium batteries containing an alkali electrolyte, the batteryvoltage thereof being about 1.2 V. For this reason, a nickel-hydrogenbattery has received attention as a higher-power battery, and also alithium battery has been developed.

The nickel-hydrogen battery works with hydrogen used as an activematerial for negative electrode. The negative electrode thereof isformed by supporting a hydrogen occlusion alloy capable of reversiblyoccluding/discharging hydrogen on the collector, and the positiveelectrode is formed by similarly supporting, for example, nickelhydroxide, which is an active material for positive electrode, on thecollector.

For example, when a negative electrode of nickel-hydrogen battery ismanufactured, predetermined amounts of hydrogen occlusion alloy powder,conductive material powder such as nickel, and binder powder such aspolyvinylidene fluoride are mixed to yield a mixed powder, to which, forexample, carboxymethyl cellulose solution is added, by which a slurry,which is a mixture for the negative electrode, is prepared. A collectorsuch as a punching Ni sheet with a desirable opening ratio, a Ni foamsheet with a desirable porosity, or a Ni powder sintered body is filledwith the slurry. The mixture is supported on the surface of thecollector and in the inside voids thereof in a contacting state bysequentially performing drying, rolling, and heat treatment.

When a positive electrode is manufactured, predetermined amounts ofnickel hydroxide powder, which is an active material for the positiveelectrode, and a conductive material such as nickel powder are mixed toyield a mixed powder, to which, a predetermined amount of, for example,carboxymethyl cellulose solution is added, and the whole mixture isagitated into a slurry form, by which a mixture for the positiveelectrode is prepared. Thereafter, a collector such as a Ni foam sheetis filled with the mixture for the positive electrode. The mixture forthe positive electrode is supported on the collector by sequentiallydrying and rolling it.

Lithium batteries are broadly classified into metallic lithium batteriesand lithium ion batteries.

For the metallic lithium battery, the negative electrode is formed ofmetallic lithium, and the positive electrode is formed by supporting anactive material for positive electrode such as LiCoO₂ on a collector.For the lithium ion battery, the positive electrode is formed in thesame manner as described above, but the negative electrode is formed bysupporting, for example, carbon (C) capable of occluding/discharginglithium ions on a collector.

In the case of the former battery of the batteries of the two types,dendrite recrystallized lithium is deposited on the surface of metalliclithium, which is the negative electrode, during charging, and it growsas the charging/discharging cycle proceeds, so that the battery cyclelife is decreased. In the worst case, the grown recrystallized lithiumbreaks a separator interposed between the positive and negativeelectrodes, sometimes causing a short circuit.

Thereupon, regarding the lithium battery, the research and developmentof a lithium ion battery incorporating a negative electrode formed bysupporting carbon on the collector is now being carried on. Thisnegative electrode does not present the problem with metallic lithiumnegative electrode during the charging/discharging cycle.

When a positive electrode of a lithium battery is manufactured,predetermined amounts of, for example, LiCoO₂ powder, which is an activematerial for the positive electrode, for example, C powder, which is aconductive material, and, for example, polyvinylidene fluoride, which isa binder, are first mixed to yield a mixed powder, to which apredetermined amount of nonaqueous solvent such as N-methylpyrrolidoneis added. The whole mixture is mixed thoroughly, by which a pastedmixture, which is a mixture for the positive electrode, is prepared.Then, the mixture is applied onto the surface of collector consisting ofmetal foil or alloy foil such as Ni, Cu and Ti--Al foil made by, forexample, rolling. Thereafter, the mixture for the positive electrode isdried to be put on the collector so as to be in firm contact andintegral with the collector.

When a negative electrode of a lithium ion battery is manufactured,fiber-form, woven cloth-form, or felt-form carbon fiber itself issometimes used as C. In general, however, predetermined amounts of Cpowder, the aforementioned binder powder, and nonaqueous solvent aremixed to prepare a pasted mixture for the negative electrode, and themixture is applied to the collector consisting of a metal foil andpressed on it after being dried.

An important point for the aforementioned the positive and negativeelectrodes is that the mixture for positive or negative electrode(hereinafter called the electrode mixture) does not peel off from thecollector when the electrode is incorporated into a battery or at thetime of a charging/discharging cycle. If the mixture peels off from thecollector, polarization begins to increase in the process ofcharging/discharging cycle, which causes the cycle life characteristicsto decrease.

When a Ni foam sheet is used as a collector as in the case of thehydrogen-nickel battery, the electrode mixture is less prone to peel offbecause it fills the inside of the sheet.

However, the pore diameter of such a foam sheet, which is about 100 μm,is too large with respect to the whole sheet. Therefore, although thispore diameter is preferable from the viewpoint of increased fillingamount of electrode mixture and useful to prevent the electrode mixturefrom peeling off, it decreases the mechanical strength of the sheet, sothat the sheet is prone to be broken. Also, the filling of electrodemixture is nonuniform, so that the electron transfer reaction in thecharging/discharging cycle is prone to be nonuniform.

When a punching metal sheet, in which openings of a predetermineddiameter are formed regularly, for example, in a zigzag lattice pattern,is used as a collector, the opening diameter is too large with respectto the whole sheet as in the case of a foam sheet, and in manufacturing,an opening-less sheet must be punched, resulting in an increase in cost.

Sometimes, an expanded metal is used as a collector. To manufacture theexpanded metal, a nonporous sheet must be subjected to specialfabrication as in the case of the punching metal sheet, so that the costof expanded metal is higher than that of the punching metal sheet.

In the case of the positive or negative electrode for a lithium battery,as described above, a metal foil usually manufactured by rolling is usedas the collector, and paste such as an electrode mixture is simplyapplied to and pressed on the smooth surface thereof, so that peelingoccurs easily.

For an electrode in which an electrode mixture is supported on bothsurfaces of the collector, it is very difficult to apply paste in thecompletely same thickness on both surfaces. The collector used isgenerally a rolled nonporous foil, so that lithium ions cannot migratefrom one surface of the collector to the other surface thereof.

Therefore, during the charging/discharging, it is impossible tocompletely use the electrode mixture supported Ion both surfaces of thecollector.

An object of the present invention is to provide a method ofmanufacturing a porous electrolytic metal foil, whereby in the processof making a metal foil by electrolytic plating, a porous metal foilstructure can be formed simultaneously with the progress of foil making.

Another object of the present invention is to provide a method ofmanufacturing a porous electrolytic metal foil, in which a porouselectrolytic metal foil, which is useful as a collector for a secondarybattery electrode, is manufactured continuously and in large quantities,and therefore at a low cost.

SUMMARY OF THE INVENTION

To achieve the above objects, the present invention provides a method ofmanufacturing a porous electrolytic metal foil, comprising the steps of:

continuously forming a metal thin layer by electrically depositing metalions on the surface of a moving cathode body by an electrolytic reactionwhich is carried out by immersing an anode body and the moving cathodebody in an electrolyte containing metal ions and by applying electriccurrent to between the anode body and moving cathode body while themoving cathode body is moved; and

continuously manufacturing an electrolytic metal foil by continuouslyseparating the metal thin layer from the surface of the moving cathodebody while the moving cathode body is moved;

and further comprising the step of:

carrying out surface treatment of the exposed surface of the movingcathode body exposed after the metal thin layer is separated by whollyor partially forming a film consisting of an electrical insulatingmaterial on the exposed surface.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic sectional view showing a typical cross-sectionalstructure of a porous electrolytic metal foil manufactured by the methodin accordance with the present invention, and FIG. 2 is a schematicsectional view showing a typical cross-sectional structure of anelectrode formed by using the metal foil shown in FIG. 1 as a collectorand by supporting an electrode mixture on both surfaces thereof.

In these figures, a metal foil 1 is formed with a plurality ofopen-pores penetrating in the thickness direction from one surface 1athereof to the other surface 1b, and the metal foil has a porousstructure as a whole.

The electrode shown in FIG. 2 has an electrode mixture 3 supported onthe surfaces 1a and 1b of the aforesaid metal foil 1. The electrodemixture 3 is supported in such a manner as to get slightly into theopen-pore 2 through an opening 2a of the open-pore 2, or in such amanner as to get considerably deep into the open-pore 2 when theopen-pore 2 has a large diameter. Alternatively, the electrode mixture 3is supported in such a manner that the electrode mixtures 3 filled inthe open-pore 2 from both surfaces of the metal foil 1 come into contactwith each other within the open-pore 2.

That is, these open-pores 2 offer an anchoring effect to the electrodemixture 3.

These open-pores 2 are formed randomly, so that not all pores arepresent as an open-pore penetrating the metal foil 1 from the surface 1ato the surface 1b, and some pores may be closed at an intermediateposition.

For this metal foil 1, it is preferable that the thickness thereof beusually 8 to 100 μm in order to obtain a foil with a porous structure.If the metal foil 1 is too thin, it may be broken in the foilmanufacturing process, described later. If it is too thick, theaforesaid open-pores are not formed.

It is preferable that the diameter of the opening 2a of the open-pore 2be within the range of 0.1 to 80 μm, though changing depending on thethickness of the metal foil 1. Also, it is preferable that 1 to 500pores be distributed per unit area (1 mm²) on the surface of the metalfoil 1.

If the diameter of the open-pore 2 is smaller than 0.1 μm, the electrodemixture 3 does not get into the pore smoothly even if the electrodemixture is applied to and pressed on the metal foil 1, so that theaforementioned anchoring effect is decreased, resulting in a decrease incontact strength between the electrode mixture 3 and the metal foil 1.If the diameter of the open-pore 2 is larger than 80 μm, the mechanicalstrength of the metal foil 1 decreases, so that the metal foil 1 isbroken, for example, when the metal foil 1 is separated from the surfaceof the moving cathode body in the metal foil manufacturing process,described later.

If the distribution density of these pores on the surfaces 1a and 1b ofthe metal foil 1 is lower than 1 pore/mm², the contact strength betweenthe electrode mixture 3 and the metal foil 1 decreases, so that theelectrode mixture is liable to peel off.

If the distribution density is higher than 500 pores/mm², though thecontact strength between the electrode mixture 3 and the metal foil 1increases, the metal foil is too porous as a whole, resulting in adecrease in mechanical strength as described above.

In the electrode manufactured by using the metal foil of the presentinvention as a collector, the electrode mixture 3 supported on thesurfaces 1a and 1b of the metal foil 1 is selected appropriatelydepending on the battery to be formed.

For example, when the intended electrode is the positive electrode for anickel-hydrogen battery, the mixture for the positive electrode, inwhich nickel hydroxide powder is used as an active material, issupported on the surfaces of the metal foil. When it is the negativeelectrode, the mixture for the negative electrode, whose principalingredient is hydrogen occlusion alloy powder, is supported.

When the intended electrode is the positive electrode for a lithiumbattery, the mixture for the positive electrode, whose principalingredient is an active material such as lithium vanadium pentoxide,lithiummanganese oxide, and lithium cobalt oxide, is supported on thesurfaces of the metal foil. When it is the negative electrode, themixture for the negative electrode, whose principal ingredient is apowder consisting of C such as chips or powder of pyrolytic carbon,coke, graphite, vitreous carbon, resin baked body, activated charcoal,and carbon fiber, is supported.

The aforementioned metal foil is manufactured continuously as a porouselectrolytic metal foil by operating the apparatus described below.

FIG. 3 is a schematic view showing a typical system used when the porouselectrolytic metal foil in accordance with the present invention ismanufactured. FIG. 4 is a schematic view showing another system.

In FIG. 3, an electrolytic bath 4 contains an electrolyte 5 containingmetal ions which are the raw material for an electrolytic metal foil tobe manufactured, an anode body 6 is disposed in this electrolyte 5, anda drum cathode body 7 facing the anode body 6 is disposed in such amanner that part of the drum cathode body 7 is immersed in theelectrolyte 5.

The anode body 6 is usually made of lead. For the moving cathode body 7,7', at least the surface thereof is made of stainless steel, Ti, Cr, Al,or Cr--Al alloy.

An electrolytic reaction is carried out by applying electric current tobetween the anode body 6 and the drum cathode body 7 while the drumcathode body 7 is rotated in the direction indicated by arrow p to movethe surface thereof successively in the electrolyte 5 and while theelectrolyte 5 is supplied continuously from a distributor 9 to a gap 8between the anode body 6 and the drum cathode body 7.

In the system shown in FIG. 4, a belt cathode body 7' is used in placeof the drum cathode body 7 shown in FIG. 3. This belt cathode body 7' iscirculated in the direction indicated by arrow p, by which the surfacethereof is moved successively in the electrolyte 5.

In the present invention, the aforementioned drum cathode body 7 andbelt cathode body 7' are called a moving cathode body because thesurface thereof on which an electrolytic metal foil is formed moves.

The metal ions are electrically deposited on the surface of the drumcathode body 7 or belt cathode body 7', where a metal thin layer iscontinuously formed so that the layer thickness increases successivelyin the moving direction of the surface of the drum cathode body 7 orbelt cathode body 7'. This metal thin layer is separated from thesurface of the drum cathode body 7 or belt cathode body 7' at a pointwhere the surface emerges from the electrolyte, and wound around atake-up roll 11 as the electrolytic metal foil 1 via rolls 10a and 10b.

In the method of the present invention, an exposed surface 7a, 7'a,which is exposed on the drum cathode body 7 or belt cathode body 7' bythe separation of the metal thin layer from the surface of the drumcathode body 7 or belt cathode body 7', is subjected to surfacetreatment, described later.

This surface treatment is carried out to form a film consisting of anelectrical insulating material on the exposed surface 7a, 7'a of themoving cathode body 7, 7'.

Specifically, the surface treatment includes,

a treatment for forming an oxide film with a thickness of at least 14 nmon the exposed surface 7a, 7'a by applying electrolytic oxidation to theexposed surface 7a, 7'a (called a first surface treatment);

a treatment for adhering an organic substance on the exposed surface 7a,7'a by spraying the organic substance onto the exposed surface 7a, 7'(called a second treatment); and

a treatment for adhering an organic substance on the exposed surface 7a,7'a by suspending the organic substance in the electrolyte (called athird treatment).

The following is a detailed description of these surface treatments.

First, the first surface treatment will be described. As shown in FIGS.3 and 4, a oxide film forming apparatus A, described later, is mountedon the exposed surface 7a, 7'a of the moving cathode body 7, 7' fromwhich the metal thin layer is separated. By operating this apparatus A,the exposed surface 7a, 7'a is electrolytically oxidized in the processbefore the exposed surface 7a, 7'a is immersed again in the electrolyte5, so that an oxide film with a thickness of at least 14 nm is formed onthe whole surface.

If the aforesaid metal thin layer is formed on the surface of the drumcathode body 7 or belt cathode body 7' with the oxide film formed on thesurface, the metal thin layer is made to have a porous structure havingopen-pores. When the electrolytic metal foil is formed by separating themetal thin layer from the moving cathode body such as the drum cathodebody 7 or belt cathode body 7', both of the surface (S surface) on themoving cathode body side and the opposite surface (M surface) becomerough. Moreover,the opposite surface becomes rougher than the surface onthe moving cathode body side.

At this time, if the formed oxide film is made thinner than 14 nm, themetal thin layer formed on the oxide film is difficult to have a properporous structure having the aforesaid open-pores and the distributiondensity thereof. This decreases the performance of metal foil as acollector on which the electrode mixture as described above is supportedwith a high contact strength.

However, if the oxide film is made too thick, the metal thin layerformed on the oxide film becomes excessively porous, by which themechanical strength thereof is decreased, so that a trouble such thatthe metal thin layer is broken when it is separated from the movingcathode body occurs frequently. Therefore, it is preferable that thethickness of the oxide film be not greater than 100 nm.

The apparatus A for forming the oxide film, which functions in theabove-described manner, on the exposed surface of the moving cathodebody includes holding means for holding an electrolytic treatment liquidfor electrolytic oxidation so that the treatment liquid is in contactwith the exposed surface of the moving cathode body; a counter electrodebody disposed in the holding means so as to oppose to the exposedsurface of the moving cathode body; and supply means for supplying theelectrolytic treatment liquid to the holding means.

This apparatus A anodizes the exposed surface by applying electriccurrent to between the moving cathode and the counter electrode bodywith the electrolytic treatment liquid supplied continuously from thesupply means to the holding means and with the electrolytic treatmentliquid in contact with the exposed surface of the moving cathode bodywhile the metal thin layer is formed on the surface of the movingcathode body by applying electric current to between the anode body andthe moving cathode body to continue electrolytic plating, withoutstopping the operation of the moving cathode body.

At this time, the operation is performed so that the operation potentialis lower in the order of the anode body, moving cathode body, andcounter electrode body. This is because if the operation potential doesnot establish the above relationship, the exposed surface of the movingcathode body is not electrolytically oxidized, so that the oxide film isnot formed there.

The oxide film may be formed continuously or intermittently using theapparatus A.

When the metal thin layer formed by electric deposition is separatedfrom the surface of the moving cathode body, part of the oxide film isremoved to the metal thin layer side at the same time, so that thethickness of the oxide film is decreased gradually by the repetition ofelectric deposition and separation. Therefore, the metal thin layerformed on the oxide film does not have the proper porous structure asdescribed above. To compensate the decreased thickness, the oxide filmmust be formed continuously or intermittently.

To operate the apparatus A, the constant current method or constantvoltage method can be used. Of these two methods, the constant voltagemethod is preferable because the part of oxide film removed from thesurface of the moving cathode body can be compensated automatically andinstantly, and the thickness of the oxide film can be prevented fromincreasing up to the unnecessary thickness.

An example A₁ of the apparatus A will be described with reference to thedrawing.

FIG. 5 is a partially cutaway perspective view showing a state in whichan apparatus A₁ is mounted on the exposed surface 7a of the drum cathodebody 7.

This apparatus A₁, having a shaft 12 for mounting the apparatus at thecenter, comprises a conductive roll 13 functioning as a counterelectrode body opposing to the drum cathode body 7 in electrolyticoxidation, electrolytic treatment liquid holding means 14 disposedaround the conductive roll 13, and a pipe which is electrolytictreatment liquid supply means 15 for supplying electrolytic treatmentliquid 15a used for electrolytic oxidation to the electrolytic treatmentliquid holding means 14. By rotatably supporting the shaft 12 bynot-illustrated means with the electrolytic treatment liquid holdingmeans 14 in contact with the exposed surface 7a of the drum cathode body7 indicated by an imaginary line, the whole of the apparatus A₁ ismounted on the exposed surface 7a of the drum cathode body 7 as shown inFIG. 3.

The conductive roll 13 may be a roll the whole of which is made of acorrosion-resistant material such as titanium, nickel, chromium, copper,and stainless steel or a roll in which the surface of the above materialis coated with a material having electric conductivity and resistance tocorrosion caused by the electrolytic treatment liquid 15a used to formthe oxide film, such as silver, silver alloy, gold, gold alloy,palladium, and palladium alloy. Also, the surface of a roll made of anon-conductive plastic material such as polypropylene or polyvinylchloride may be covered with foil, wire, or mesh of a material havingelectric conductivity and corrosion resistance. Alternatively, amaterial having electric conductivity and corrosion resistance may beplated, thermally sprayed, or applied to the surface of theaforementioned roll. To sum up, a roll at least the surface of which haselectric conductivity and corrosion resistance is used as a counterelectrode body for electrolytic oxidation on the surface of the drumcathode body.

The electrolytic treatment liquid holding means 14 surrounding theconductive roll (counter electrode body) 13 has a proper elasticity aswell as permeability. The electrolytic treatment liquid holding means 14is formed by covering the outer periphery of the conductive roll 13 witha material having resistance to corrosion caused by the electrolytictreatment liquid used, such as felt, nonwoven fabric cloth, or splityarn of polyurethane, polyvinyl formal, or polyester.

Above the electrolytic treatment liquid holding means 14, the pipe 15formed with a plurality of openings 15b in the axial direction of theelectrolytic treatment liquid holding means 14 is disposed aselectrolytic treatment liquid supply means, and the predeterminedelectrolytic treatment liquid 15a is supplied to the pipe 15 by means ofa pump 15c. The supplied electrolytic treatment liquid 15a is notsubject to any special restriction, and a liquid which does not have anadverse effect on the manufacture of metal thin layer even if beingmixed with the electrolyte used for the manufacture of metal thin layeris used. For example, a liquid which is the same as the electrolyte usedat present to make metal electrically deposit on the surface of the drumcathode body, or a liquid which has the same components as those of theelectrolyte but a different ratio of components can be used.

As the electrolyte, for example, copper sulfate solution is used inmanufacturing electrolytic copper foil, and nickel sulfate solution ornickel sulfamate solution is used in manufacturing electrolytic nickelfoil. Also, in manufacturing electrolytic aluminum foil, AlCl₃ --LiAlH₄-tetrahydrofuran bath and NaF.2Al(C₂ H₅ O)₃.4toluene bath, which aredisclosed in Japanese Patent Publication No. 48-4460, and the like canbe used.

As the electrolytic treatment liquid 15a, a liquid which does notcontain ions of metal deposited on the drum cathode body 7 can also beused. Such electrolytic treatment solutions include an acidic solutionsuch as sulfuric acid solution, phosphoric acid solution, andhydrochloric acid solution and a neutral solution in which sodiumsulfate, potassium sulfate, sodium hydrochloride, potassiumhydrochloride, etc. are dissolved. Among these, sulfuric acid solutionis preferably used in manufacturing electrolytic copper foil by usingcopper sulfate electrolyte.

The supply means for the electrolytic treatment liquid 15a is notlimited to the above-mentioned pipe-form means. For example, theconductive roll 13 is made hollow, many openings Bare formed on theperipheral surface thereof, and the electrolytic treatment liquid 15a issupplied to the hollow portion of the conductive roll 13, by which theelectrolytic treatment liquid 15a may be supplied to the electrolytictreatment liquid holding means 14 from the inside thereof through theopenings on the peripheral surface of the conductive roll 13.

When the apparatus A₁ is used, the oxide film is formed on the exposedsurface 7a of the drum cathode body 7 in the following manner.

First, the electrolytic treatment liquid holding means 14 of theapparatus A₁ is elastically brought into contact with the exposedsurface 7a of the drum cathode body 7 rotating in the directionindicated by arrow p. Thereupon, the electrolytic treatment liquidholding means 14 rotates automatically in the direction indicated byarrow r in FIG. 5. With this state being kept, a predeterminedelectrolytic treatment liquid 15a is supplied to the pipe (electrolytictreatment liquid supply means) 15.

The electrolytic treatment liquid 15a drips onto the electrolytictreatment liquid holding means 14 from the openings 15b, permeates intothe electrolytic treatment liquid holding means 14, and is kept therein.As a result, the conductive roll (counter electrode body forelectrolytic oxidation) 13 and the exposed surface 7a of the drumcathode body 7 becomes conductive via the electrolytic treatment liquid15a.

Then, terminals 13a, 13a attached to the conductive roll 13 areconnected to the minus side of a power supply (not shown), and theexposed surface 7a of the drum cathode body 7 is connected to the plusside of the power supply so that an electrolytic current flows betweenthe conductive roll 13 and the exposed surface 7a of the drum cathodebody 7, whereby the exposed surface is anodized. At this time, theconductive roll (counter electrode body) 13 is operated so that thepotential becomes to be lower than the potential of the drum cathodebody in the electrolytic bath on which surface is formed a metal thinlayer, and at the same time, the potential of the anode body positionedin the electrolytic bath is made higher than that of the drum cathodebody. If the potential of the drum cathode body is higher than that ofthe anode body, there occurs a problem such that metal is notelectrically deposited on the surface of the drum cathode body, or aproblem such that if electric current is applied so that the potentialof the conductive roll is higher than that of the drum cathode body, theconductive roll 13 is made the plus electrode, and the exposed surface7a of the drum cathode body 7 is made the minus electrode, so that theexposed surface 7a of the drum cathode body 7 is not electrolyticallyoxidized.

By properly selecting the rotational speed of the drum cathode body 7,the operation potential of the conductive roll (counter electrode body),and the like, an oxide film with a desirable thickness is formed on theexposed surface 7a.

In this apparatus A₁, it is preferable that the width of theelectrolytic treatment liquid holding means 14 is smaller than that ofthe drum cathode body 7 so that both side portions 7b, 7b on the exposedsurface 7a of the drum cathode body 7 are not electrolytically oxidized.

The reason for this is as follows: The metal thin layer directly formedat these portions 7b, 7b has a higher mechanical strength than theporous metal thin layer formed on the oxide film produced by theapparatus A₁. Therefore, when the metal thin layer is separated from thedrum cathode body, a trouble of breaking of the metal thin layer in theprocess of separation can be prevented by starting the separation fromthe portion of metal thin layer formed at the portions 7b, 7b.

FIG. 6 is a partially cutaway perspective view showing a state in whichanother apparatus A₂ is mounted on the exposed surface 7a of the drumcathode body 7.

In the case of this apparatus A₂, the electrolytic treatment liquidholding means 16 is a box-shaped vessel whose one face is open, and thisopening 16a is disposed in liquid-tight slidable contact with or closeto the exposed surface 7a of the drum cathode body 7. Therefore, theportions of sides 16b, 16b of the vessel 16, which are in slidablecontact with or close to the exposed surface 7a of the drum cathode body7, are curved so as to match the curvature of the exposed surface 7a ofthe drum cathode body 7.

The width of the vessel 16 is smaller than that of the drum cathode body7 for the same reason as that in the case of the electrolytic treatmentliquid holding means 14 for the apparatus A₁, so that both side portions7b, 7b of the exposed surface 7a of the drum cathode body 7 are notelectrolytically oxidized.

It is preferable that the vessel 16 be made of a material which isresistant to corrosion caused by the electrolytic treatment liquid used,such as polyvinyl chloride and polypropylene.

In the case where the vessel 16 is disposed so as to be in slidablecontact with the exposed surface 7a of the drum cathode body 7, it ispreferable that the vessel 16 be made of a material havingwear-resistance, lubricity, and elasticity, such as polyethylene,polyester, polyurethane, and silicone rubber. In this vessel 16, acounter electrode body 17 for electrolytic oxidation, which is made of,for example, titanium or stainless steel, is disposed. This counterelectrode body 17 faces the exposed surface 7a of the drum cathode body7 exposed to the interior of the vessel 16 through the opening 16a ofthe vessel 16.

A supply pipe 18a for electrolytic treatment liquid is attached to theside wall of the vessel 16, and a discharge pipe 18b for electrolytictreatment liquid is attached to the top wall thereof, these pipesconstituting electrolytic treatment liquid supply mean 18. Theelectrolytic treatment liquid used to form an oxide film is suppliedinto the vessel 16 through the supply pipe 18a to fill the vessel 16,covers the exposed surface 7a of the drum cathode body 7, and flows outof the system through the discharge pipe 18b.

Electric current is applied to between the counter electrode body 17 andthe drum cathode body 7 while allowing the electrolytic treatment liquidto flow in the vessel 16, by which the exposed surface 7a of the drumcathode body which is exposed to the interior of the vessel 16 throughthe opening 16a can be electrolytically oxidized.

If the vessel 16 is mounted so that some clearance is formed between theopening 16a of the vessel 16 and the exposed surface 7a of the drumcathode body 7, part of the supplied electrolytic treatment liquid flowsout along the exposed surface 7a of the drum cathode body 7 through theclearance, so that an electrolytic treatment liquid film with a uniformthickness is formed on the exposed surface 7a of the drum cathode bodywhich is exposed to the interior of the vessel 16 through the opening16a, by which the forming condition of oxide film is preferablystabilized.

For the electrolytic treatment liquid supplied into the vessel 16, theelectrolyte used for manufacturing a metal thin layer is usually used asit is by being pumped up.

FIG. 7 and FIG. 8, which is a sectional view taken along the lineVIII--VIII of FIG. 7, are views showing a state in which anotherapparatus A₃ is mounted on the exposed surface of the drum cathode body.

This apparatus A₃ has electrolytic treatment liquid holding meansconsisting of a trough-shaped vessel 19. For this trough-shaped vessel19, the upper part is open, and both of the ends 19a, 19a in thelengthwise direction are sealed. One end 19a is provided with a supplypipe 20 for electrolytic treatment liquid, constituting electrolytictreatment liquid supply means. One side 19b of the trough-shaped vessel19 is lower in height than the other side 19c.

The length of the trough-shaped vessel 19 is shorter than the width ofthe drum cathode body 7 for the same reason as that in the case of theelectrolytic treatment holding means 15 of the apparatus A₁ so that bothside portions 7b, 7b of the exposed surface 7a of the drum cathode body7 are not electrolytically oxidized.

The trough-shaped vessel 19 is mounted so that the lengthwise directionthereof agrees with the width direction of the drum cathode body 7, andthe one side 19b is close to the exposed surface 7a of the drum cathodebody so as to form some clearance between the side 19b and the exposedsurface 7a of the drum cathode body.

A counter electrode body 17 is disposed on the other side 19c of thetrough-shaped vessel 19, and a metal powder removing filter 21 isinterposed between the counter electrode body 17 and the exposed surface7a of the drum cathode body. As a result, the interior of thetrough-shaped vessel 19 is divided into a space 19d where the counterelectrode body 17 is disposed and a space 19e positioned on the side ofthe exposed surface 7a of the drum cathode body.

The metal powder removing filter 21 prevents metal powder fromdepositing on the exposed surface 7a of the drum cathode body 7, themetal powder being deposited on the exposed surface 7a of the drumcathode body 7 by a process in which the metal contained in theelectrolytic treatment liquid is electrically deposited abnormally asmetal powder on the surface of the counter electrode body 17 in theelectrolytic treatment, and the metal powder is removed from the counterelectrode body by the flow of electrolytic treatment liquid.

The electrolytic treatment liquid supplied to the trough-shaped vessel19 through the supply pipe 20 overflows over the side 19b after fillingthe trough-shaped vessel 19, and flows down along the exposed surface 7aof the drum cathode body rotating in the direction indicated by arrow p.In this process, therefore, an electrolytic treatment liquid film with auniform thickness is continuously formed on the exposed surface 7a ofthe drum cathode body.

For the electrolytic treatment liquid, the electrolyte used formanufacturing a metal thin layer may be used as it is. Alternatively,electrolytic treatment liquid supply pipes connecting with the spaces19d and 19e formed in the trough-shaped vessel 19 may be disposedseparately so that, for example, the electrolyte used for manufacturinga metal thin layer is supplied to the space 19d and an electrolyte witha different composition or containing no metal ions is supplied to thespade 19e.

The cross-sectional shape of the trough-shaped vessel 19 is not limitedto a triangular one as shown in FIGS. 7 and 8. The shape may be apolygon such as quadrangle and hexagon or a semicircle. In effect, thetrough-shaped vessel 19 may be shaped so that the electrolytic treatmentliquid filling the vessel 19 overflows over the side 19b so that aliquid film can be formed on the exposed surface 7a of the drum cathodebody.

FIG. 9 and FIG. 10, which is a sectional view taken along the line X--Xof FIG. 9, are views showing a state in which still another apparatus A₄is mounted on the exposed surface of the drum cathode body.

This apparatus A₄ has electrolytic treatment liquid holding means 22consisting of an elongated closed vessel of a convex lens shape in crosssection.

Specifically, an attaching portion 22b of a counter electrode body 17for electrolytic oxidation is mounted at the 114 back of a curved plate22a in a liquid tight manner, both ends 22C, 22C in the lengthwisedirection are sealed, a supply pipe 23 for electrolytic treatment liquidis attached to a substantially central position of vessel, andelectrolytic treatment liquid spraying means 22d is formed at the tipend of the curved plate 22a, by which the electrolytic treatment liquidsupply means for supplying electrolytic treatment liquid onto theexposed surface 7a of the drum cathode body 7 is formed. The sprayingmeans 22d may consist of, for example, a plurality of holes formed alongthe lengthwise direction of the curved plate 22a or a slit with apredetermined width formed in the lengthwise direction of the curvedplate 22a.

The length of the closed vessel 22 is shorter than the width of the drumcathode body 7 for the same reason as that in the case of theelectrolytic treatment holding means 15 of the apparatus A₁ so that bothside portions 7b, 7b of the exposed surface 7a of the drum cathode body7 are not electrolytically oxidized.

The whole vessel is so configured that the counter electrode body 17 isdisposed at the attaching portion 22b, the lengthwise direction of thevessel agrees with the width direction of the drum cathode body 7, andspraying means 22d formed in the curved plate 22a is disposed so as toface the exposed surface 7a of the drum cathode body 7 with apredetermined gap.

The electrolytic treatment liquid fed into the vessel 22 through thesupply pipe 23 by pumping etc. is sprayed from the spraying means 22dafter filling the vessel 22 to hit the exposed surface 7a of the drumcathode body 7 rotating in the direction indicated by arrow p, and flowsdown along the exposed surface 7a, whereby a liquid film with a uniformthickness is formed.

As the electrolytic treatment liquid, the electrolyte used formanufacturing a metal thin layer may be used, and if necessary, anotherelectrolyte such as dilute sulfuric acid solution may be used.

While this state is maintained, a predetermined voltage is applied tobetween an anode of the drum cathode body 7 and a cathode of the counterelectrode body 17, by which the exposed surface 7a of the drum cathodebody is electrolytically oxidized. Since the drum cathode body 7 isrotated in the direction indicated by arrow p in the figures, an oxidefilm is formed continuously or intermittently on the exposed surface 7a.

Although in this apparatus A₄, the surface opposing to the exposedsurface 7a of the drum cathode body is curved, the shape is not limitedto this one, and any shape such that the electrolytic treatment liquidfilling the vessel interior can be sprayed toward the exposed surface 7aof the drum cathode body may be used. Also, means for uniformlydistributing the electrolytic treatment liquid, for example, means inwhich uniform small holes are formed in a pipe and the electrolytictreatment liquid supplied to this pipe is sprayed from these small holesmay be provided within the vessel 22. Further, the supply pipe 23 is notnecessarily attached to the central position of the apparatus A₄, butmay be attached to any position where the electrolytic treatment liquidcan be sprayed uniformly from the spraying means 22d.

Also, a metal powder removing filter may be provided between the counterelectrode body 17 and the spraying means 22d as in the case of theapparatus A₃ so as to prevent the metal powder electrically deposited onthe counter electrode body from flowing out onto the exposed surface 7aof the drum cathode body 7.

This apparatus A₄ achieves an effect that when the electrolyte formanufacturing a metal thin layer, which has a relatively high metalconcentration, is used as the electrolytic treatment liquid, the amountof electrolyte used can be decreased by making the spray opening of thespraying means 22d smallest possible, and the deposition of metal saltin the electrolytic treatment liquid used can be inhibited to the utmostby decreasing the amount of scattered electrolyte.

For example, when an electrolytic copper foil is manufactured by usingcopper sulfate electrolyte, copper sulfate solution having a relativelyhigh copper concentration is used as an electrolyte. When thiselectrolyte is used as an electrolytic treatment liquid for forming anoxide film, copper sulfate crystals are produced if the temperature islow, and stick to the apparatus and the electrolytic copper foil,thereby inhibiting the smooth operation of the apparatus. In theapparatus A₄ shown in FIGS. 9 and 10, this trouble can be eliminatedeasily by merely changing the shape of the spraying means 22d and thedistance from the spraying means 22d to the exposed surface 7a of thedrum cathode body.

Next, a second surface treatment will be described.

In this treatment, by spraying an organic substance onto the exposedsurface of moving cathode body, the exposed surface is partially coveredwith a film formed by the organic substance adhering on the exposedsurface in a speck form.

Specifically, a resin liquid of any kind is sprayed onto the exposedsurface of moving cathode body, and then the resin is cured. The sprayedresin liquid turns into minute liquid drops and sticks onto the exposedsurface of moving cathode body in a speck form, and is cured on theexposed surface. As a result, a film consisting of hardened particles ofthe liquid drops is formed on the exposed surface of moving cathodebody.

The film formed at this time is not a dense resin film of the resinconstituting the resin liquid used, but is formed by the hardenedparticles of the resin adhering discontinuously onto the exposed surfaceof moving cathode body.

Therefore, when electric current is applied to between the movingcathode body and the anode body to carry out electrolytic reaction,electric deposition is inhibited at the portions of the hardenedparticles, so that the metal thin layer formed on this film becomesporous.

The organic substance used for forming this film is not subject to anyspecial restriction, and may be any organic substance which iselectrically insulating and capable of being sprayed. A resin liquid inwhich a resin such as polyester, epoxy resin, polyamide, andpolyurethane is dissolved in an appropriate solvent can be used.

Also, by appropriately selecting the spraying conditions such asspraying pressure, diameter of nozzle used for spraying, and dischargeamount of resin liquid, the size and distribution density of thehardened particles are changed, whereby the porosity of this film, andin turn, the porosity of metal thin layer formed on the film can beregulated.

In a third surface treatment, an organic substance is suspended in theelectrolyte.

In the apparatuses shown in FIGS. 3 and 4, the anode body 6 is usuallyformed of a material insoluble in electrolyte, such as lead, so that alarge quantity of oxygen gas is generated from the surface of the anodebody 6 when electric current is applied, and heavily agitates theelectrolyte flowing between the anode body 6 and the moving cathode body7, 7'. Therefore, if an organic substance is added to the electrolyte inthe course of electrolytic plating, the organic substance is dispersedand suspended in a particulate form in the electrolyte being agitated.

The organic substance used in this treatment may be any organicsubstance which is electrically insulating, insoluble in electrolyte,and suspended in a particulate state in electrolyte. For example,various machine oils or insulating oils are used.

In this treatment, when the moving cathode body is moved and immersed inthe electrolyte, the aforesaid organic it substance, which is dispersedand suspended in a particulate state in the electrolyte, adheres to theexposed surface. As a result, particulates of organic substance areformed in a row on the exposed surface of moving cathode body, so that amicroscopically porous film is formed.

Since electric current is applied to between the moving cathode body andthe anode body in this process, the metal thin layer formed on this filmalso becomes porous for the same reason as described regarding thesecond surface treatment.

At this time, by appropriately selecting the kind of the suspendedorganic substance, suspension concentration, and the like, the porosityof film, and in turn, the porosity of metal thin layer formed on thefilm can be regulated.

On the surface of metal foil thus manufactured, a preservative film maybe formed, if necessary, for actual use by using an organic preservativesuch as benzotriazole or an inorganic preservative such as chromatetreatment liquid.

Also, if, for example, a silane coupling agent is applied onto thesurface of manufactured metal foil, the contact strength between theelectrode mixture and the metal foil can be enhanced when the electrodemixture is supported on the surface of metal foil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a typical cross-sectional structureof a metal foil manufactured by a method in accordance with the presentinvention;

FIG. 2 is a sectional view of a typical electrode with a collector usinga metal foil manufactured by a method in accordance with the presentinvention;

FIG. 3 is a schematic view showing a manufacturing system for anelectrolytic metal foil;

FIG. 4 is a schematic view showing another manufacturing system;

FIG. 5 is a partially cutaway perspective view showing a state in whichan apparatus A₁ used for forming an oxide film is mounted on the exposedsurface of a drum cathode body;

FIG. 6 is a partially cutaway perspective view showing a state in whichan apparatus A₂ used for forming an oxide film is mounted on the exposedsurface of a drum cathode body;

FIG. 7 is a partially cutaway perspective view showing a state in whichan apparatus A₃ used for forming an oxide film is mounted on the exposedsurface of a drum cathode body;

FIG. 8 is a sectional view taken along the line VIII--VIII of FIG. 7;

FIG. 9 is a partially cutaway perspective view showing a state in whichan apparatus A₄ used for forming an oxide film is mounted on the exposedsurface of a drum cathode body; and

FIG. 10 is a sectional view taken along the line X--X of FIG. 9.

BEST MODE OF CARRYING OUT THE INVENTION WORKING EXAMPLES 1 AND 2,COMPARATIVE EXAMPLES 1 AND 2

1) Manufacture of metal foil

In the system shown in FIG. 3, the drum cathode body 7 was made oftitanium, and the apparatus A₄ shown in FIGS. 9 and 10 was mounted onthe surface of the drum cathode body 7.

The electrolyte 5 with a copper ion concentration of 100 g/liter, asulfuric acid concentration of 100 g/liter, and a bath temperature of60° C. was supplied into the electrolytic bath 4. While the drum cathodebody 7 was rotated, an electric current with a current density of 60A/dm² was applied to between the drum cathode body 7 and the anode body6 to continuously form a copper thin layer on the surface of the drumcathode body 7. By separating the copper thin layer from the surface ofthe drum cathode body 7, the electrolytic copper foil 1 was manufacturedcontinuously.

While the manufacture of the electrolytic copper foil 1 was continued,the aforesaid electrolyte was supplied into the closed vessel 22 throughthe supply pipe 23 of the apparatus A₄, and sprayed onto the exposedsurface 7a of the drum cathode body 7 rotating in the directionindicated by arrow p from the spraying means 22d while the voltagebetween the drum cathode body 7 and the counter electrode body (made oftitanium) 17 was kept at a constant value of 50 V.

A titanium oxide film with a thickness of 70 nm was formed continuouslyon the exposed surface 7a of the drum cathode body 7.

Copper was electrically deposited on this titanium oxide film to form acopper thin layer. By continuously separating the copper thin layer fromthe drum cathode body 7, the electrolytic copper foil 1 was obtained.

Then, the obtained electrolytic copper foil 1 was subjected to surfaceroughening with a current density of 30 A/dm² by using an electrolytewith a copper ion concentration of 20 g/liter, a sulfuric acidconcentration of 40 g/liter, and a bath temperature of 30° C.

For the electrolytic copper foil after surface roughening, the averagethickness was 50 μm, and the surface roughnesses (Rz) of the separationsurface (S surface) from the drum cathode body and the opposite surface(M surface) were 5 μm and 11 μm, respectively.

Also, in this electrolytic copper foil, open-pores communicating in thethickness direction were found. The diameter of the open-pore was 0.1 to3 μm, and the distribution density thereof was 100 to 200 pores/mm².

2) Manufacture of electrode

Ten parts by weight of polyvinylidene fluoride powder was mixed with 100parts by weight of KETJEN BLACK EC(carbon black manufactured by KETJENBLACK INTERNATIONAL CO., LTD. and sold by LION AKZO CO., LTD., specificsurface area: 950 m² /g, average grain size: 0.03 μm), and 30 parts byweight of N-methylpyrrolidone was added to the resultant mixed powder toprepare paste of active material mixture.

This paste was applied to both of the surfaces of the aforesaidelectrolytic copper foil, dried, and press-formed at a pressure of 2000kg/cm² to manufacture a working example electrode 1 of 100 μm thick, 10mm wide, and 20 mm long. The amount of active material mixture supportedon this electrode was 20 mg.

A working example electrode 2 was manufactured in the same way as in thecase of the working example electrode 1 except that the electrolyticcopper foil was manufactured while forming a titanium oxide film of 14nm thick on the exposed surface 7a of the drum cathode body 7 byapplying a constant voltage of 10 V to between the counter electrodebody 17 and the drum cathode body 7 when the oxide film was formed.

For the electrolytic copper foil used for this working example electrode2, the average thickness was 50 μm, the Rz of S surface was 2 μm, the Rzof M surface was 10 μm, the diameter of open-pore was 0.1 to 3 μm, andthe distribution density thereof was 20 to 40 pores/mm².

For comparison, a rolled copper foil of 50 μm thick was prepared, and 20mg of an active material mixture was put on both of the surfaces thereofin the same way as described above to manufacture a comparative exampleelectrode 1.

Also, both of the surfaces of the aforesaid rolled copper foil wereroughened to about Rz 2 to 5 μm with #800 emery paper, i;, and 20 mg ofan active material mixture was put thereon in the same way as in theworking examples to manufacture a comparative example electrode 2.

3) Cycle life of electrode

An electrolyte formed by dissolving lithium perchlorate of 1 M inpropylene carbonate of 1 kg was prepared. Each of the aforesaidelectrodes was disposed in this electrolyte as a negative electrode, andmetallic lithium foils were disposed as a counter electrode and areference electrode, by which four kinds of three-electrode cells wereassembled.

Then a charging/discharging cycle test was made. In one cycle of thistest, a constant current of 1.2 mA was applied to the aforesaidthree-electrode cell to perform charging until the voltage reached 0 Vwith respect to the potential of the reference electrode, the currentapplication was halted for 20 minutes, and then discharging wasperformed with a constant current of 1.2 mA until the voltage reached1.5 V with respect to the potential of the reference electrode.

For each three-electrode cell, the discharge capacity at the 20th cyclein the charging/discharging cycle test was compared with the dischargecapacity at the 1st cycle, and the ratio (%) of the former to the latterwas calculated. The result is given in Table 1.

                  TABLE 1                                                         ______________________________________                                                       Ratio of discharge capacity in                                                charging/discharging cycle test                                               (%: 20th cycle/1st cycle)                                      ______________________________________                                        Working example electrode 1                                                                    97 or higher                                                 Working example electrode 2                                                                    About 80                                                     Comparative example electrode 1                                                                About 40                                                     Comparative example electrode 2                                                                About 70                                                     ______________________________________                                    

As is apparent from the above result, the discharge capacity of theworking example electrode is less prone to decrease in the process ofcharging/discharging cycle, so that the working example electrodes haveexcellent cycle life characteristics.

The reason for this is that because the collector (electrolytic copperfoil) has a porous structure of the aforesaid specification, the contactstrength between the collector and the active material mixture supportedon the collector is high, so that the active material mixture iseffectively prevented from peeling off in the process of thecharging/discharging cycle test. Also, the reason for this is thought tobe that because the electrolytic copper foil is porous and open-porespenetrate the foil in the thickness direction, lithium ions pass throughthe open-pores between the active material mixtures supported on thesurfaces, so that a uniform electron transfer reaction proceeds.

WORKING EXAMPLE 3

The apparatus A₃ shown in FIGS. 7 and 8 was mounted on the exposedsurface of a titanium-made drum cathode body. An electrolytic copperfoil was manufactured while a 35 nm thick titanium oxide film was formedon the exposed surface 7a of the drum cathode body 7 by applying aconstant voltage of 25 V to between the counter electrode body 17 andthe drum cathode body 7. The resultant electrolytic copper foil wassubjected to surface roughening under the same conditions as in the caseof the working example electrode 1.

The obtained electrolytic copper foil had a porous structure in whichthe average thickness was 25 μm, the Rz of S surface was 2 μm, the Rz ofM surface was 9 μm, the diameter of open-pore was 0.1 to 3 μm, and thedistribution density thereof was 150 to 250 pores/mm².

A collector with an average thickness of 50 μm whose surface consistedof the M surface was formed by lapping the electrolytic copper foil overanother with their S surfaces being brought into contact with eachother, and an active material mixture was put on the M surfaces in thesame way as in the case of the working example electrode 1, by which aworking example electrode 3 was manufactured.

This electrode was subjected to the same charging/discharging cycle testas in the case of the working example electrode 1.

This electrode showed a value of 98% or higher of the ratio of dischargecapacity at the 20th cycle to discharge capacity at the 1st cycle,exhibiting excellent cycle life characteristics.

WORKING EXAMPLE 4

The apparatus A₁ shown in FIG. 5 was mounted on the exposed surface of atitanium-made drum cathode body. An electrolytic copper foil wasmanufactured while a 70 nm thick titanium oxide film was formed on theexposed surface 7a of the drum cathode body 7 by applying a constantvoltage of 50 V to between the conductive roll 13 and the drum cathodebody 7.

The obtained electrolytic copper foil had a porous structure in whichthe average thickness was 20 μm, the Rz of S surface was 2 μm, the Rz ofM surface was 6 μm, the diameter of open-pore was 0.1 to 3 μm, and thedistribution density thereof was 350 to 450 pores/mm².

After an active material mixture was put on the M surface and S surfaceof this electrolytic copper foil in such a manner that the ratio ofamount of mixture supported on the M surface to that on the S surface is9:1, the electrolytic copper foil was lapped over another with their Ssurface sides being brought into contact with each other in the same wayas in the case of the working example electrode 3, and the lapped foilswere dried and press-formed at a pressure of 2000 kg/cm², by which aworking example electrode 4 was manufactured.

This electrode was subjected to the same charging/discharging cycle testas in the case of the working example electrode 1.

This electrode showed a value of 99% or higher of the ratio of dischargecapacity at the 20th cycle to discharge capacity at the 1st cycle,exhibiting excellent cycle life characteristics.

WORKING EXAMPLE 5

Commercially available lithium carbonate (Li₂ CO₃) and basic cobaltcarbonate (2CoCO₃.3Co(OH)₂) were weighed so that the molar ratio ofLi/CO is 1:1, and wet-blended using ethanol with a zirconia-made ballmill. Thereafter, the blended material was heat-treated at a temperatureof 900° C. for two hours to synthesize LiCoO₂.

This LiCoO₂ was ground into powder with an average grain size of 16μmwith the ball mill, and 6 parts by weight of graphite powder with anaverage grain size of 0.1 μm was blended with 100 parts by weight ofthis powder. Further, 3.5 parts by weight of polyvinylidene powder wasdissolved in 30 parts by weight of N-methylpyrrolidone, and theresultant material was added to the aforesaid mixed powder of LiCoO₂powder and graphite powder to prepare paste of active material mixture(electrode mixture).

Using this paste and using the electrolytic copper foil shown in theworking example electrode 1 as a collector, a working example electrode5 with the active material mixture of 20 mg was manufactured in the sameway as in the case of the working example electrode 1.

This electrode was subjected to the same charging/discharging cycle testas in the case of the working example electrode 1.

This electrode showed a value of 98% or higher of the ratio of dischargecapacity at the 20th cycle to discharge capacity at the 1st cycle,exhibiting excellent cycle life characteristics.

WORKING EXAMPLE 6

In working example 1, the electrolyte was replaced with an electrolytefor manufacturing electrolytic nickel foil, having a nickel sulfateconcentration of 300 g/liter, a boric acid concentration of 40 g/liter,and a bath temperature of 60° C., and this electrolyte was used to forma 70 nm thick titanium oxide film on the exposed surface of drum cathodebody by using the apparatus A₄. While forming this titanium oxide film,an electrolytic nickel foil was manufactured with a current density of30 A/dm².

The obtained electrolytic nickel foil had a porous structure in whichthe average thickness was 25 μm, the Rz of S surface was 2 μm, the Rz ofM surface was 7 μm, the diameter of open-pore was 0.1 to 4 μm, thedistribution density thereof was 300 to 400 pores/mm², and the porositywas 5%.

Hydrogen occlusion alloy powder with a composition of MmNi₃.55 Mno₀.4Al₀.3 Co₀.75 (Mm: misch metal) and a grain size of 30 to 50 μm wasprepared. Five parts by weight of 60% fluid dispersion ofpolytetrafluoroethylene powder and 30 parts by weight of 1.2%carboxymethylcellulose solution were mixed with 100 parts by weight ofthis alloy powder to prepare paste.

This paste was applied to both of the surfaces of the aforesaid twonickel foils, and one nickel foil was lapped over the other with their Ssurface sides being brought into contact with each other. After beingdried, the lapped foils were press-formed at a pressure of 2000 kg/cm²,by which a negative electrode for nickel-hydrogen battery with athickness of 0.8 mm, a width of 70 mm, and a length of 100 mm wasmanufactured.

Meanwhile, a publicly known positive electrode with a thickness of 0.8mm, a width of 70 mm, and a length of 100 mm was prepared. In thispositive electrode, nickel hydroxide was used as an active material forthe positive electrode, and the theoretical discharge capacity was setat a value about 0.7 times of the theoretical discharge capacity ofaforesaid negative electrode. Separators of 0.2 mm thick made of nylonwere interposed between four positive electrodes and five negativeelectrodes, and a 6NKOH electrolyte was used to assemble anickel-hydrogen battery with a rated capacity of 10 Ah.

This battery was subjected to a charging/discharging cycle test, inwhich one cycle consists of 120% overcharging at 0.5 C and dischargingdown to a final discharge voltage of 1.0 V at 1.0 C, and the decreaseratio of discharge capacity at 500 cycle time was measured.

For comparison, negative electrodes were manufactured as a comparativeexample electrode 3 and comparative example electrode 4 by using apunching nickel sheet foil with an opening ratio of 10% and a nickelfoam with a porosity of 50% as collectors, respectively, and by puttinga mixture on the collector under the same conditions as described above,and nickel-hydrogen batteries were assembled. On these batteries aswell, the decrease ratio of discharge capacity at 500 cycle time wasmeasured in the same way as in the working example. The results aregiven in Table 2.

In addition, the tensile strength and elongation of the collector weremeasured by the method specified in JIS C6511, and the measured value isgiven in Table 2. Also, the manufacturing cost of the comparativeexample electrode, which is calculated when the manufacturing cost ofthe working example electrode 6 is taken as 1, is given as a relativevalue in Table 2.

                  TABLE 2                                                         ______________________________________                                        Decrease ratio  Mechanical properties                                         of discharge    of collector                                                  capacity        Tensile           Manufacturing                               (%: after       strength Elongation                                                                             cost                                        500 cycles)     (kg/mm.sup.2)                                                                          (%)      (relative value)                            ______________________________________                                        Working 15          25       7      1                                         example                                                                       electrode 6                                                                   Comparative                                                                           20          15       5      3                                         example                                                                       electrode 3                                                                   Comparative                                                                           24           5       1      10                                        example                                                                       electrode 4                                                                   ______________________________________                                    

As is apparent from the above result, a battery incorporating anelectrode in which a metal foil of the present invention is used as acollector has a low decrease ratio of discharge capacity, and therebyhas high cycle life characteristics. Also, the collector has highmechanical properties, so that, for example, breakage or like trouble isnot caused even when the collector is contained in the battery by beingwound. Because the collector is manufactured by electrolytic plating, itcan be mass-produced, so that the manufacturing cost can be reduced,which contributes to the provision of inexpensive electrodes.

WORKING EXAMPLES 7 AND 8

When the electrolytic copper foil of working example 1 was manufactured,the resin liquid described below was sprayed onto the exposed surface 7aof the drum cathode body 7 under the following conditions.

Composition of resin liquid: RIPOXY R-804B (trade name, a resinmanufactured by Showa Highpolymer Co., Ltd.) 96.5 wt %, PERMERIC (tradename, a hardening agent manufactured by Showa Highpolymer Co., Ltd.) 3wt %, Hardening Accelerator D (trade name, manufactured by ShowaHighpolymer Co., Ltd.) 0.5 wt %

Spraying: Pressure Sprayer No. 7760 (trade name, a pressure-type sprayermanufactured by Furupla Co., Ltd.)

After the resin liquid was hardened, electrolytic plating was performedunder the same conditions as those in working example 1 to form a copperthin layer on the hardened film. By separating the copper thin layer, anelectrolytic copper foil was manufactured.

For the obtained electrolytic copper foil, the average thickness was 10μm, the Rz of S surface was 1.5 μm, and the Rz of M surface was 2.5 μm.In the thickness direction, open-pores with a diameter of 0.1 to 80 μmwere found with a distribution density of 1 to 5 pores/mm² on thesurface.

Without surface roughening, 20 mg of the electrode mixture of workingexample 1 was put on both of the surfaces of this electrolytic copperfoil to manufacture a working example electrode 7.

Also, in working example 1, an electrolytic copper foil was manufacturedby performing electrolytic plating under the same conditions as those inworking example 1 except that FBK-RO220 (trade name, a machine oilmanufactured by Mitsubishi Oil Co., Ltd.) was suspended with aconcentration of 100 g/m³ in electrolyte.

For the obtained electrolytic copper foil, the average thickness was 10μm, the Rz of S surface was 1.5 μm, and the Rz of M surface was 2.3 μm.In the thickness direction, open-pores with a diameter of 0.1 to 60 μmwere found with a distribution density of 1 to 10 pores/mm² on thesurface.

Without surface roughening, 20 mg of the electrode mixture of workingexample 1 was put on both of the surfaces of this electrolytic copperfoil to manufacture a working example electrode 8.

For comparison, without surface treatment on the exposed surface of thedrum cathode body, a copper thin layer was formed directly on theexposed surface under the conditions for electrolytic plating in workingexample 1, and then separated to manufacture an electrolytic copperfoil.

For the obtained electrolytic copper foil, the average thickness was 10μm, the Rz of S surface was 1.5 μm, and the Rz of M surface was 2.5 μm.In the thickness direction, no pores were found.

Without surface roughening, 20 mg of the electrode mixture of workingexample 1 was put on both of the surfaces of this electrolytic copperfoil to manufacture a comparative example electrode 5.

By using these electrodes, the same three-electrode cells as in workingexample 1 were assembled, and a charging/discharging cycle test was madeunder the same conditions. The result is given in Table 3.

                  TABLE 3                                                         ______________________________________                                                       Ratio of discharge capacity in                                                charging/discharging cycle test                                               (%: 20th cycle/1st cycle)                                      ______________________________________                                        Working example electrode 7                                                                    About 80                                                     Working example electrode 8                                                                    About 85                                                     Comparative example electrode 5                                                                About 60                                                     ______________________________________                                    

As is apparent from the above result, since the working exampleelectrodes 7, 8 have a collector (electrolytic copper foil) of a porousstructure, the discharge capacity is unlikely to decrease in the processof charging/discharging cycle, so that these electrodes have high cyclelife characteristics.

INDUSTRIAL APPLICABILITY

The metal foil manufactured by the method in accordance 4"" with thepresent invention has many open-pores formed in the thickness direction.

Therefore, when this metal foil is used as a collector for a secondarybattery, the openings of these open-pores have an anchoring effect onthe electrode mixture supported on the metal foil, so that the contactstrength between the electrode mixture and the collector is increased,by which the electrode mixture is prevented from peeling off in thecharging/discharging cycle.

Also, when this metal foil is used as a collector for the electrode oflithium battery, the electron transfer reaction in battery operationproceeds smoothly via the open-pores of this metal foil, so that thecoefficient of use of active material is increased, by which the cyclelife characteristics of battery is improved.

Since this metal foil is manufactured by electrolytic plating, it can bemass-produced, so that the manufacturing cost is decreased, whichcontributes greatly to the manufacture of inexpensive electrodes.

What is claimed is:
 1. A method of manufacturing a porous electrolytic metal foil, comprising:immersing an anode body and a cathode body in an electrolyte containing metal ions and applying electric current to between the anode body and the cathode body while continuously moving the cathode body through the electrolyte to continuously form a thin metal layer by electrically depositing the metal ions on a surface of the cathode body; continuously separating said thin metal layer from the surface of said cathode body, while said cathode body is moving so as to form an exposed surface on said cathode body; and contacting the exposed surface of said cathode body with an organic, electrically insulating substance to carry out a surface treatment to adhere said organic substance to said exposed surface so as to partially cover said exposed surface with a film.
 2. The method of manufacturing a porous electrolytic metal foil according to claim 1, wherein said surface treatment is carried out to make said organic substance adhere to said exposed surface by spraying said organic substance onto said exposed surface.
 3. The method of manufacturing a porous electrolytic metal foil according to claim 1, wherein said surface treatment is carried out to make said organic substance adhere to said exposed surface by suspending said organic substance in said electrolyte.
 4. The method of manufacturing a porous electrolytic metal foil according to claim 1, wherein said electrolytic metal foil has a structure comprising open-pores with a diameter of 0.1 to 80 μm which are formed in the thickness direction and said open-pores have a distribution density of 1 to 500 pores/mm² on the surface thereof.
 5. The method of manufacturing a porous electrolytic metal foil according to claim 4, wherein the organic substance is a resin liquid.
 6. The method of manufacturing a porous electrolytic metal foil according to claim 5, wherein the resin is selected from the group consisting of a polyester, an epoxy resin, a polyamide and a polyurethane.
 7. The method of manufacturing a porous electrolytic metal foil according to claim 3, wherein the organic substance is a machine oil or an insulating oil.
 8. The method of manufacturing a porous electrolytic metal foil according to claim 1, wherein the anode body comprises lead.
 9. The method of manufacturing a porous electrolytic metal foil according to claim 8, wherein said surface of the cathode body comprises stainless steel, Ti, Cr, Al or a Cr--Al alloy.
 10. The method of manufacturing a porous electrolytic metal foil according to claim 9, wherein the electrolyte comprises a solution selected from the group consisting of a copper sulfate solution, a nickel sulfate solution, a nickel sulfamate solution, an AlCl₃ --LiAlH₄ -tetrahydrofuran bath and a NaF.2Al(C₂ H₅ O₃).4 toluene bath.
 11. The method of manufacturing a porous electrolytic metal foil according to claim 1, wherein the electrolyte comprises copper.
 12. The method of manufacturing a porous electrolytic metal foil according to claim 6, wherein the anode body comprises lead; said surface of the cathode body comprises stainless steel, Ti, Cr, Al or a Cr--Al alloy and the electrolye comprises a solution selected from the group consisting of a copper sulfate solution, a nickel sulfate solution, a nickel sulfamate solution, an AlCl₃ --LiAlH₄ -tetrahydrofuran bath and a NaF.2Al(C₂ H₅ O₃).4 toluene bath.
 13. The method of manufacturing a porous electrolytic metal foil according to claim 7, wherein the anode body comprises lead; said surface of the cathode body comprises stainless steel, Ti, Cr, Al or a Cr--Al alloy and the electrolye comprises a solution selected from the group consisting of a copper sulfate solution, a nickel sulfate solution, a nickel sulfamate solution, an AlCl₃ --LiAlH₄ -tetrahydrofuran bath and a NaF.2Al(C₂ H₅ O₃).4 toluene bath. 